Until now, several proposals have been brought out in order to utilize proteins from both vegetal and animal origin, as a renewable source of polymeric raw materials to make compositions which have a thermoplastic behaviour and, consequently, are able to perform like a thermoplastic under the high temperature and shear forces exerted by an extruder in a conventional process of extrusion-cooking or injection molding. Many shaped articles are thereby obtained what witnesses the great interest in substituting, as primary raw materials, the known synthetic petroleum derived thermoplastics (as for instance PET, PVC, PA, PP, PS, HDPE, LDPE etc.) in some of their performances, by other environmentally friendly materials which are save for humans, animals and the environment. Films, food containers, pet chews, cutlery and warehouse articles are some of the actual commodities whose formerly plastic raw forming material is being currently supplanted by new protein-based thermoplastic compositions to make them edible and/or biodegradable.
There are several patent documents which are representative of the mentioned technologies as, for example, U.S. Pat. No. 4,076,846, where an edible, water-soluble thermoplastic molding composition is proposed, comprising a starch material, a plant or animal derived protein salt or mixtures thereof, water, an edible plasticizer, an edible lubricant and other additives which are mixed up while heating and, afterward, introduced into the heated barrel of an extruder where the composition is mixed under pressure and then extruded through a die, to render a film, or subsequently injected into a mold to obtain a shaped article.
The document U.S. Pat. No. 5,397,834 proposes a biodegradable water-resistant and edible thermoplastic composition made up by aldehyde-starch and proteins either from plant (zein) or animal source, utilizing water as a plasticizer and some other substances as glycerine and polyols; the patent of the same author, U.S. Pat. No. 5,523,293, describes a thermoplastic composition based on soy protein (combined or not with other plant or animal proteins) compounded by mixing a soy protein isolate with water, a plasticizer, a starch and a reducing agent.
The document U.S. Pat. No. 5,569,482 describes a process for producing an edible proteinaceous film by extruding within a biaxial extruder a melted compound of protein (soya) and water along with alternative additives such as plasticizers, a saccharide, fat and oils.
In the document DE19712400 a homogeneous hydroplastic mass is obtained by submitting a mixture of collagen powder and water to elevated temperatures and shear forces inside a extruder and processed to obtain a granulate, strands or sheets.
In the document ES2001119 a thermoplastic material, on the base of a raw material substantially constituted by scraps of tanned hides from the footwear industry, is obtained by subjecting the coarsely particulated hides to a high static pressure of between 200-900 bar inside a mold, followed by heating until reaching, under the same initial or lower pressure, the temperature of 50 to 250° C.
The document U.S. Pat. No. 5,922,379 brings out a biodegradable protein/starch/natural cellulosic fiber thermoplastic composition where the use of cellulosic fibers (including crosslinkers) as reinforcement therein, reduce the overall composition cost and enhance toughness, thermal and strength properties and water resistance. In the patent of the same author, U.S. Pat. No. 6,379,725, there is proposed a protein-based thermoplastic composition containing a mixture of plant and animal derived proteinic material along with water (up to 16 wt %), edible plasticizer and various additive and nutrient ingredients, which by injection molding renders solid articles with possess properties close to those of synthetic polymers such as good strength and hardness. In the patent of the same author, U.S. Pat. No. 6,455,083, an edible thermoplastic composition comprising a mixture of plant and animal derived protein, starch, water (up to 20 wt %), edible fiber and metallic salt hydrate along with edible plasticizers and a variety of additives is described.
The document WO0183597 proposes a biodegradable zein thermoplastic resin made up by zein protein and fatty acids which is thermically transformable into shaped articles.
The document WO0145517 describes an edible thermoplastic made of a mixture of both plant and animal derived proteins along with starch, water, edible cellulose fiber and other additives to be transformed into pet chews by injection molding.
The document U.S. Pat. No. 5,665,152 provides a method of forming a non-edible biodegradable grain protein-based solid, which is the extrusion product of a resin (POLYTRITICUM) basically formulated from soy protein isolates and concentrates, wheat and corn gluten and mixtures thereof, along with a minor amount of water (up 14% by weight), starch, plasticizers and a reducing agent to improve the rheology and final properties, and extruding the mixture under heating and share avoiding the temperature within the extruder barrel to overpass 80° C.
In the patent application US20020119224, a variety of resins, including starch, proteins (casein, denatured or partially hydrolized collagen), thermoplastic polymers such as poly (ethylene acrylic acid) and poly (ethylene vinyl alcohol) and mixtures thereof, are combined along with water, a multiplicity of additives, amongst them rawhides, to obtain, by extrusion or injection molding, a molded animal chew toy.
All the techniques above described are intended to fabricate shaped articles on the base of proteinic materials by formulating compositions which are capable of having a thermoplastic-like behaviour when undergoing a process of extrusion-cooking, from which high temperatures and shear forces are suffered by said compounded formulations, for the necessary period of time to render a melted homogeneous plastic-like material, what allows its further conformation into shaped bodies by pressing it through a slotted die or by injecting it into a mold.
Apart from the need of applying important amounts of heating during the mixture preparation and extrusion-cooking process, there is sometimes necessary, in addition, to heat the molds and, in either case after the extruding or molding processes it will be always necessary to coot the shaped mass below its glass transition temperature for the melt to solidify and thus to obtain a solid body before the unmolding process.
The cost of energy, in terms of the spent power to drive the process, and the needed heat applied in the successive steps of the same, linked to the different outputs, which respectively depends on the mass rheology and the kind of mold processing, determines the efficiency of this kind of techniques. The flowability of melted proteinic compounds within the extrusion molding equipments is mostly lower than that of synthetic polymers under similar conditions. Therefore the output of protein-based compound processing is generally low as compared with the conventional plastics.
Until now, molding techniques that are intended to utilize natural polymers, like proteins, as a renewable raw material to substitute plastics in forming utilities, are based on the thermoplastic ability of that natural polymeric materials under certain physical conditions (extrusion-cooking) and linked to the presence of certain coadjuvant substances (fundamentally water).
Moreover, in the particular case of collagen protein, other kinds of processes to transform collagen or collagen-rich raw materials into molded or coated utilities having an artificial, leather-like surface are those which consist of melting the powdered leather or isolated collagen along with a synthetic polymer. The processes so far described in the literature for producing leather-like products on the basis of natural polymer materials such as collagen are limited to the procedure of blending the collagen-powder (obtained by different techniques) with the synthetic resins by submitting the mixture to the melting temperature of the thermoplastic resin or to the curing conditions of a thermoset resin.
Powdered scraps of natural leather or collagen-rich by-products (splits) coming from industrial leather manufacture, are mixed together with synthetic thermoplastic or thermoset polymeric resins as a base material, in order to compound a mixture which is able to undergo an extrusion molding process or any other conventional molding process to render solid shaped articles or coatings providing a leather-like surface and enhancing the physic-mechanical properties with respect to that of natural leather or the resins alone. The leather or collagen powder can impart an appearance, feel, and functions resembling those of leather, to a covering layer or molded article formed together with a synthetic resin. To meet this requirement, various proposals have been made, as for instance in patent EP0421450, in which a collagen powder such as a leather fiber powder or a leather powder formed by pulverizing leather scraps is used together with a synthetic polymeric resin such as a polyurethane resin, a polyester resin, a polyacrylic resin, a polyvinyl chloride resin or a polyolefin, or a synthetic rubber such as an SB rubber, to form a covering layer on the surface of an automobile interior trim, a construction interior material, furniture, etc, or to form a molded article such as a steering wheel cover of an automobile, whereby performances resembling those of natural leather are imparted thereto.
Some other examples of the prior art set forth above, and using either thermoplastic or thermoset resins can be found in patents: JP62181741, JP63099914, JP1156047, JP3124800, JP3195800, JP4226538, EP0470399, JP5132868, JP5222681, JP6017378, JP6330472, JP9104841, JP10212675 and U.S. Pat. No. 6,800,384.
In this particular industry, some very important advances in the manufacture of leather-like surface coverings or molded articles would lie on the possibility of lowering production costs and moreover making the products become edible, fully biodegradable in the short or medium term and recyclable, by suppressing the need of using slowly or non biodegradable synthetic resins.
In the light of these facts, after an extensive investigation and trials, the authors of the present invention have now surprisingly found that some proteins can exhibit a thermoset behaviour when, an essentially dry protein is combined with an essentially anhydrous alcohol and submitted to a discrete amount of heat, that is, a moderate elevation of temperature during a relatively short period of time.
Further, it has now been surprisingly found in accordance with the present invention that when a powder of a dry and finely ground protein-rich raw material (the particle size being preferably less than 50 μm) from which the water has been thoroughly removed or at least with such a low residual content of water that avoids this water to be available for taking part in the process, is homogeneously mixed with a certain amount of an anhydrous and liquid alcohol at environmental temperature, in such an extent that at least a self-cohesion of the mixture is reached, and a plastic moldable mass is obtained, such described mass can perform as a thermoset material, and can be thermally inducted to set in some few seconds by the addition of certain amount of heat.
This surprising thermosetting property brings about outstanding advantages in the field of protein-based biodegradable and/or edible solid shaped articles manufacturing. One of the main advantages is the great simplicity of both the compound formulation and the process for carrying out its transformation into a solid object. This advantage along with the lower energetic cost of the process, as compared with thermoplastic processing, makes this technique very useful to transform highly proteinaceous materials into edible and biodegradable utilities.
Particularly, the present invention has the advantages of a) simplifying the manufacturing process for leather-like coverings and molded products manufacturing and, therefore, allowing to reduce production costs, since it cheapens the equipment and facilities, shortens the process times and reduces the expenditures for raw materials and energy, b) rendering biodegradable recyclable and edible molded articles which are suitable to substitute many of those manufactured on the basis of synthetic resins, c) incorporating advantageous physical and mechanical properties as for instance good moisture absorption and release, viscoelasticity, thermosealability and the ability of being transformed into shaped articles like a thermoplastic. Particularly, products obtained of setting collagen compositions will not shrivel or deform after extreme folding and, after pressing, twisting, stretching or squeezing, they always recover their original shape.